In some cases, an actuator having a haptic feedback to provide a user with a tactile sensation is incorporated into a touch screen of a tablet terminal, a flat-type keyboard without key traveling, a touch-type operation switch without a keystroke or the like. Conventionally, an electromagnet, a piezoelectric element, a vibration motor or the like has been used as a driving part of an actuator. However, in recent years, a shape memory alloy (SMA), which has better performances in vibration intensity, response, and size, has become the more popular choice.
In an impact-driven actuator, a vibration intensity given to a vibrator is able to be adjusted by using the wave crest value and pulse width of a single pulse voltage applied to the SMA. It is, however, difficult to adjust an output of a DC-DC converter, which functions as a power source, according to a user's favorite haptic sense since the adjustment leads to a complicated circuit. Moreover, the adjustment of the pulse width changes the displacement amount of the impact-driven actuator, and thus changes the frequency of acceleration. The change in the frequency of acceleration leads to a change in the feeling of vibration on a finger, and therefore sometimes it is required to adjust the vibration intensity without changing the frequency of acceleration.
Consequently, it would be preferable to provide an improved apparatus for driving an actuator.